1. Field of Invention
The present invention relates generally to catheter systems used in diagnosis and treatment of various body tissues and, more specifically, to ablation systems for ablating cardiac tissue in the treatment of electrophysiological diseases.
2. Description of the Related Art
As is well know, catheters provide medical professionals access to various interior regions of the human body in a minimally invasive manner. In such a way, catheters are tremendous medical tools in support of diagnosis and treatment of different tissues of the body. Catheters allow such professionals to place one or more medical instruments, pharmacological agents or other matter at a target tissue site. For example, in cardiac procedures in support of diagnosis and treatment of atrial fibrillation, catheters provide access to various chambers of the heart, carrying ablation devices which translate therein to such sites for ablation of specific cardiac tissue associated with atrial fibrillation.
Ablation of tissue, cardiac tissue for example, is typically directly related to the orientation of the ablation element, from which energy sufficient to ablate biological tissue is emitted, with respect to a target tissue site. For such procedures, precise control of the ablation device is desirable to ensure proper placement of the ablation element utilized in creation of one or more desired lesions. As an electrophysiologist, or other medical professional, manipulates the proximal end of the catheter system, the distal end of the catheter must be responsive to such movement in a very predetermined, smooth-flowing and proportional way.
Additionally, the orientation of the ablation device, from which ablative energy is emitted and directed toward the target tissue, differs with the modality utilized for the procedure. For example, with tip electrode RF based devices, the tip must be properly placed in direct contact with the target tissue. For creation of numerous intermediate lesions along a desired lesion path, the tip electrode must be moved across the target tissue surface in a controlled fashion, which is often difficult due to inconsistencies of the tissue surface. Under certain conditions, the tip may act to impede movement across the surface of the target tissue, causing the tip to erratically jump or skip across the tissue in an undesirable way.
For example, for the treatment of atrial flutter, it is often desirable to ablate the isthmus which lies between the inferior vena cava and the tricuspid valve. The contour of this tissue, while generally curvilinear, is irregular and inconsistent, comprising various peaks and valleys, which differ from individual to individual. Ablating tissue in this region often requires the precise and controlled placement of the distal tip of the ablation device. Because of the curvilinear nature of the isthmus, it has been found to be difficult to lay down a straight long linear ablation element to ablate this area. This task is complicated by the fact that the steering or guiding system of the ablation system typically directly impacts the approach and orientation of the tip upon the tissue, which further impairs the ability of the system to transmit sufficient ablative energy for proper tissue ablation. Furthermore, due to the desired depth of the ablation required at this location, proper placement of the ablation device is critical to the creation of a desired long continuous deep lesion therein.
Proper placement of an ablation device is also exasperated by the fact that some ablative energy technologies require energy transmission conduits which are bulky, or otherwise constructed from materials less flexible, making the distal portion of the catheter difficult to properly position. For example, distal portions of optical fiber or microwave based ablation systems, or catheter systems comprising an endoscopic device, may be more difficult to maneuver due to the lack of flexibility in the transmission mediums utilized therein. As should be readily apparent, when the distal portion of an ablation catheter system is not properly positioned, ablative energy is not properly directed and applied to the target tissue, resulting in poor lesion formation. It is therefore essential that the ablative device be able to be manipulated and sufficiently controlled to be properly positioned to transfer the requisite energy to ablate biological tissue and create a desired lesion therein.
Accordingly, it is a general object of the present invention to provide an ablation system which resolves the above-identified problems. Another object of the present invention is to provide an ablation system which ensures proper placement of an ablation device upon a target tissue to be ablated. Yet another object of the present invention is to provide an ablation system incorporating a deflectable ablative device which can emit a relatively uniform energy pattern therefrom. Another object of the present invention is to provide an ablation system to ablate tissue, forming a lesion therein which is substantially independent of an azimuth or approach angle. Still another object of the present invention is to provide an ablation system to easily and effectively ablate the isthmus between the inferior vena cava and the tricuspid valve without the need for a precise deflection system. Yet another object of the present invention is to provide a catheter system which ensures proper placement of an ablation device proximate a target tissue site during creation of a long continuous lesion.
These and other objects are achieved through systems disclosed herein. More specifically, a system for ablating a selected portion of biological tissue at a target tissue site is provided. The system is particularly suitable to ablate cardiac tissue, as well as other soft tissues of the body, and includes a tubular member having a distal end including an ablative device which, in turn, includes one or more ablation elements adapted to emit ablative energy therefrom, and a steering system operably attached to a proximal section. The distal end of the tubular member is configured to be deflected into a predetermined geometric shape wherefrom a relatively uniform energy pattern is emitted, such that tissue ablation can occur substantially independent from an approach angle defined between the tubular member and the target tissue surface. In this way, for example, with a substantially side-firing ablation device one could bend or otherwise deflect the ablation device into a specific shape to obtain a uniform energy distribution about the distal end of the ablation device.
In one embodiment, the ablation device includes at least one ablation element adapted to emit ablative energy therefrom. The ablation device is configured to engage tissue from one of many approach angles while maintaining proper ablative energy transfer to the tissue resulting in tissue ablation and the creation of one or more desired lesions.
In another embodiment, the ablation device includes at least one flexible ablation element adapted to emit ablative energy therefrom. The at least one ablation element is configured to deflect along with the tubular member. Alternatively, the ablation device may include at least one ablation element having a geometric configuration which allows deflection of the distal end of the ablation device.
In still another embodiment, the ablation device may also include a shielding means adapted to be opaque with respect to the corresponding ablative energy utilized, protecting tissues surrounding a target tissue site from the ablative energy. Additionally, the shielding means may be configured to reflect at least a portion of the ablative energy toward the target tissue site to facilitate or encourage tissue ablation and lesion formation.
In still another embodiment, the tubular member of the ablation device translates within a tubular guiding member, the distal portion of the ablation device is adapted to include a preformed shape. As the ablation device emerges from the distal opening of the guiding member, the distal portion assumes its preformed curvilinear shape. The preformed shape may be selected to facilitate the emission of a uniform energy pattern therefrom.
In another embodiment, the ablation device is a catheter system wherein the tubular member is elongated to facilitate entry into a patient""s vascular system and advancement to a target tissue site, a cardiac muscle site for example.
The ablative energy is preferably electromagnetic energy in the microwave range. However, other suitable tissue ablation energies include, but are not limited to, cryogenic, ultrasonic, laser, chemical and radiofrequency.
In yet another embodiment, the ablation device is a microwave antenna assembly which includes an antenna configured to emit microwave ablative energy. The ablation device may also include a shielding means coupled to the antenna assembly. The shielding means may be adapted to substantially shield a surrounding area of the antenna from the electromagnetic field radially generated therefrom while permitting a majority of the field to be directed generally in a predetermined direction toward the target tissue site. Alternatively, the shielding means, in another embodiment, may be adapted to absorb the electromagnetic energy transmitted therefrom protecting surrounding tissues. The ablation device may further include an insulator which functions to hold the shielding means and antenna in fixed relationship with respect to each other and a target tissue site, further controlling the ablative characteristics of the ablation device.
In yet another embodiment, the steering system is part of an elongated guiding member having at least one lumen passing therethrough, the tubular member of the catheter translating therein.
In another aspect of the present invention, a method for treatment of a Heart includes entering the ablative device into a patient""s vasculature; guiding the distal end of the ablation device into a chamber of the patient""s heart; manipulating the ablation device until the distal end is proximate a target tissue site; applying ablative energy from an energy source to the ablation device.
In one embodiment, the manipulating is performed by incrementally advancing the ablative device along a plurality of positions along an ablation path to produce a substantially continuous lesion.
In another embodiment, the step of manipulating is performed by incrementally sliding, or otherwise moving, the ablative device along a predefined ablation path to produce a long and substantially continuous lesion.
In yet another embodiment, the step of sliding includes the step of positioning the ablative device in an overlapping arrangement with respect to prior ablation sites along the ablation path.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.